Problem: $-\dfrac{7}{8} + \dfrac{1}{2} = {?}$
Explanation: $ = - {\dfrac{7 \times 1}{8 \times 1}} + {\dfrac{1 \times 4}{2 \times 4}} $ $ = - {\dfrac{7}{8}} + {\dfrac{4}{8}} $ $ = - \dfrac{{7} + {4}}{8} $ $ = -\dfrac{3}{8}$